PURPOSE: To provide automatic saw blade guide width adjusting method and apparatus for a band saw machine, which can automatically adjust the saw blade guide space according to the width of a work.

CONSTITUTION: As photoelectric switches (non-contact sensor) 13, 45 are provided on a movable stock vice 11 of a main body stock vice 3 and a movable side saw blade guide 35, respectively, when the photo detecting side photoelectric switch 45 provided on the movable side saw blade guide 35 is positioned in the position of the light emitting side photoelectric switch 13 of a movable stock vice 11 moved for fixing a work W, the photo detecting side photoelectric switch 45 is operated. A hydraulic cylinder 39 (saw blade guide moving device) and a piston rod 41 are provided to move the movable side saw blade guide 35, and if the movable side saw blade guide 35 is positioned in the position where the agreement of positions of both photoelectric switches 13, 45 by the operation of the photo detecting side photoelectric switch 45 is detected, a cutting area corresponding to the width of the work can be set.